1. Field of the Invention
The present invention relates to an extension fixture and, more particularly, to an extension fixture for a turning tool.
2. Description of the Related Art
A conventional extension fixture for a turning tool in accordance with the prior art shown in FIGS. 6 and 7 comprises a shank 20, a pull rod 30, and a clamping sleeve 40. The shank 20 has an inside formed with a passage 21 having a first end formed with an engaging recess 22. The engaging recess 22 of the shank 20 has a distal end formed with a tapered guide face 23. The pull rod 30 is rotatably mounted in the passage 21 of the shank 20 and has a first end formed with a rotation head 31 rested on a second end of the passage 21 of the shank 20 and a second end formed with an outer thread 32 extended into the engaging recess 22 of the shank 20. The rotation head 31 of the pull rod 30 is driven by a drive tool (not shown), such as a screwdriver or the like, so as to rotate the pull rod 30. The clamping sleeve 40 is movably mounted in the engaging recess 22 of the shank 20 and has a first end formed with a screw bore 41 screwed onto the outer thread 32 of the pull rod 30 and a second end formed with a clamping recess 42 for clamping a turning tool 10 (see FIG. 6). The clamping recess 42 of the clamping sleeve 40 has a peripheral wall formed with a plurality of elongated slits 44 so that the clamping recess 42 of the clamping sleeve 40 is flexible. The second end of the clamping sleeve 40 has an outer face formed with a tapered guide face 43 rested on the tapered guide face 23 of the shank 20.
In operation, the turning tool 10 is initially received in the clamping recess 42 of the clamping sleeve 40. Then, the rotation head 31 of the pull rod 30 is driven by a drive tool to rotate the pull rod 30 which is rotated to move the clamping sleeve 40 inwardly relative to the shank 20 by engagement between the outer thread 32 of the pull rod 30 and the screw bore 41 of the clamping sleeve 40. When the clamping sleeve 40 is moved inwardly, the tapered guide face 43 of the clamping sleeve 40 is pressed by the tapered guide face 23 of the shank 20 to contract the clamping recess 42 of the clamping sleeve 40 so as to clamp the turning tool 10 in the clamping recess 42 of the clamping sleeve 40.
However, the pull rod 30 is not positioned in place, so that the pull rod 30 is easily unscrewed from the clamping sleeve 40 due to a reaction produced during operation of the turning tool 10. Thus, the clamping sleeve 40 is easily loosened from the pull rod 30 and moved outwardly relative to the shank 20, so that the turning tool 10 is not clamped in the clamping sleeve 40 closely and easily produce a vibration during operation of the turning tool 10. Thus, the turning tool 10 is easily broken due to the vibration, thereby decreasing the lifetime of the turning tool 10.